But the school claims it has improved, saying its current problems are simply a result of a change in management staffing.
"We have just got a new chief executive, and the school is still in the process of getting the new systems and paperwork in place," said marketing manager Eva Chen.
"NZQA knows this, but still decided to close the school down without giving us a chance and without considering the interest of our students."
Graphic design tutor Joyce Liu, 35, said the announcement came as a total shock, as staff were told only on Wednesday that the school was to be closed down the next day.
"Students who are sitting their final papers are now facing the possibility that they have to start all over again," Ms Liu said.
zAuthority chief executive Karen Poutasi said St George had been visited and reviewed three times since 2010, and there were "serious concerns" about the school's ability to provide high-quality education.
She said the authority proceeded to cancel its registration when it could not provide any adequate reason why the school should remain registered.
An authority report in February said the school had a single active company director, who was based offshore, and several changes in staffing, leadership and processes had been made since a new chief executive was appointed last year.
Student numbers had also fallen, from about 300 in 2010 to 12 this year.
Yesterday, authority staff were at the school's Queen St premises to meet staff and help students to find new schools to finish their studies.
Students were told the authority will work with Public Trust to refund or transfer their remaining fees and with Immigration on visa issues.
But Taiwanese student Howard Huang, 22, said all enrolled students had signed a petition to back the school and are insisting on completing their courses at St George.
"Some of us have only one more paper before graduating, and all of us are happy with our course at St George," said Mr Huang, who paid $32,000 in fees for his two-year graphic design course.
"NZQA says it is targeting the school, but we, the students, are the real victims."